The present disclosure relates generally to photodisruption induced by a pulsed laser beam and the location of the photodisruption so as to treat a material, such as a tissue of an eye. Although specific reference is made to cutting tissue for surgery such as eye surgery, embodiments as described herein can be used in many ways with many materials to treat one or more of many materials, such as cutting of optically transparent materials.
Cutting of materials can be done mechanically with chisels, knives, scalpels and other tools such as surgical tools. However, prior methods and apparatus of cutting can be less than desirable and provide less than ideal results in at least some instances. For example, at least some prior methods and apparatus for cutting materials such as tissue may provide a somewhat rougher surface than would be ideal. Pulsed lasers can be used to cut one or more of many materials and have been used for laser surgery to cut tissue.
Examples of surgically tissue cutting include cutting the cornea and crystalline lens of the eye. The lens of the eye can be cut to correct a defect of the lens, for example to remove a cataract, and the tissues of the eye can be cut to access the lens. For example the cornea can be to access the cataractous lens. The cornea can be cut in order to correct a refractive error of the eye, for example with laser assisted in situ keratomileusis (hereinafter “LASIK”) or photorefractive keratectomy (hereinafter “PRK”), for example.
Many patients may have visual errors associated with the refractive properties of the eye such as nearsightedness, farsightedness and astigmatism. Astigmatism may occur when the corneal curvature is unequal in two or more directions. Nearsightedness can occur when light focuses before the retina, and farsightedness can occur with light refracted to a focus behind the retina. There are numerous prior surgical approaches for reshaping the cornea, including laser assisted in situ keratomileusis (hereinafter “LASIK”), all laser LASIK, femto LASIK, corneaplasty, astigmatic keratotomy, corneal relaxing incision (hereinafter “CRI”), Limbal Relaxing Incision (hereinafter “LRI”), photorefractive keratectomy (hereinafter “PRK”) and Small Incision Lens Extraction (hereinafter “SMILE”). Astigmatic Keratotomy, Corneal Relaxing Incision (CRI), and Limbal Relaxing Incision (LRI), corneal incisions are made in a well-defined manner and depth to allow the cornea to change shape to become more spherical.
Cataract extraction is a frequently performed surgical procedure. A cataract is formed by opacification of the crystalline lens of the eye. The cataract scatters light passing through the lens and may perceptibly degrade vision. A cataract can vary in degree from slight to complete opacity. Early in the development of an age-related cataract the power of the lens may increase, causing nearsightedness (myopia). Gradual yellowing and opacification of the lens may reduce the perception of blue colors as those shorter wavelengths are more strongly absorbed and scattered within the cataractous crystalline lens. Cataract formation may often progresses slowly resulting in progressive vision loss.
A cataract treatment may involve replacing the opaque crystalline lens with an artificial intraocular lens (IOL), and an estimated 15 million cataract surgeries per year are performed worldwide. Cataract surgery can be performed using a technique termed phacoemulsification in which an ultrasonic tip with associated irrigation and aspiration ports is used to sculpt the relatively hard nucleus of the lens to facilitate removal through an opening made in the anterior lens capsule. The nucleus of the lens is contained within an outer membrane of the lens that is referred to as the lens capsule. Access to the lens nucleus can be provided by performing an anterior capsulotomy in which a small round hole can be formed in the anterior side of the lens capsule. Access to the lens nucleus can also be provided by performing a manual continuous curvilinear capsulorhexis (CCC) procedure. After removal of the lens nucleus, a synthetic foldable intraocular lens (IOL) can be inserted into the remaining lens capsule of the eye.
Prior short pulse laser systems have been used to cut tissue, and have been used to treat many patients. However, the prior short pulse systems may provide less than ideal results in at least some instances. For example, the alignment of the eye with the laser surgery system can be less than ideal in at least some instances, such as when refractive treatment of the cornea of the eye is combined with a treatment of the lens of the eye such as removal of the cortex and nucleus from the eye.
Further, proper alignment of the IOL within the eye can play an important role in achieving satisfactory results. At least some prior laser surgery systems can provide less than ideal results when used to place an intraocular lens in the eye to treat aberrations of the eye such as low order aberrations comprising astigmatism or higher order aberrations. While accommodating IOLs can correct refractive error of the eye and restore accommodation, the prior accommodating IOLs can provide less than ideal correction of the astigmatism of the eye. For cataract patients with an astigmatism, toric IOL's provide the potential for better uncorrected visual acuity after surgery. However, toric IOLs pose significant challenges for a treating physician because even small errors in an IOL's position may significantly affected the patient's visual acuity. For every one degree of error in a toric IOL's rotational alignment, there is a 3.3 percent decrease in the correction of astigmatism. Roach, L., “Toric IOLs: Four Options for Addressing Residual Astigmatism,” Cataract, April 2012, pp. 29-31. As such, there is a need for systems and methods for improving the accuracy of the placement of the IOL within the eye.
Although prior systems have attempted to combine laser eye surgery systems with data from eye measurement devices, the results can be less than ideal in at least some instances. The surgical eye can be altered as compared with the natural eye, and anatomical structures of the surgical eye may not coincide with anatomical structures of the eye prior to surgery. For example, the cornea can be distorted during surgery, for example from contact with the patient interface or from alternation of the surface of the cornea. Also, the eye can undergo cyclotorsion when moved from one measurement system to another measurement system such that alignment of the angle of the eye can be less than ideal. Also, the pupil of the eye during surgery can differ from the pupil of the eye that would be used for normal vision, which can make alignment of the eye with surgical incisions and intraocular lenses more challenging than would be ideal. For example, in at least some instances the pupil of the eye can dilate and affect the location of the center of the pupil.
There are other factors that may limit the usefulness of data provided to a surgical laser from eye measurement devices such as tomography and topography systems. For example, there can be at least some distortion of at least some of the images taken among different devices, and this distortion can make the placement of laser incisions less than ideal in at least some instances. Also, the use of different systems for measurement and treatment can introduce alignment errors, may take more time that would be ideal, and may increase the cost of surgery such that fewer patients than would be ideal can receive beneficial treatments.
At least some prior ophthalmic laser surgery systems can be less than ideally suited for combination with prior topography systems. For example, prior laser surgery systems for cutting the cornea may rely on a patient interface that can make measurements of the cornea less than ideal in at least some instances. The prior patient interfaces may apply force to the eye, for example with a suction ring that engages the eye near the limbus. The resulting force can distort the corneal shape and decrease accuracy of the corneal measurements in at least some instances. The distortions of the cornea related to placement of the patient interface can limit the accuracy of corneal measurements and alignment of the corneal surgical procedures. Also, the images obtained with prior laser systems configured to couple to the eye with patient interfaces can be distorted at least partially in at least some instances, which can make combination of the images from prior laser surgery system with prior eye measurement systems such as corneal topography and tomography systems less than ideal in at least some instances.
In light of the above, it would be desirable to provide improved methods and apparatus that overcome at least some of the above limitations of the above prior systems and methods. Ideally, these improved systems and methods will provide improved alignment with the eye during surgery, improved placement of laser beam pulses to incise the eye, improved placement of refractive incisions of the eye, improve placement of incisions for intraocular lenses, corneal topography from the laser surgery system without distorting the corneal shape, and integration of the measurement data with the laser treatment parameters, in order to provide an improved result for the patient. Ideally, the laser surgery system would also provide for a more accurate manner of placing the IOL within the patient's eye.